Piezoelectric ultrasonic motor

ABSTRACT

A piezoelectric ultrasonic motor includes a piezoelectric stator including a metal tube with an inner space and piezoelectric elements mounted on the outer circumference of the metal tube, a rotary shaft including a rotation bar inserted into the inner space of the metal tube, and a rotation member provided around the rotation bar in contact with the piezoelectric stator. The piezoelectric stator strains with an electric field applied thereto, and the rotation member rotates in response to the strain of the piezoelectric stator. A power transmission member is provided at one portion of the rotation bar to transmit the rotation of the rotation member to an object to be transported. With face contact the motor achieves stable actuation together with enhanced force and sufficient strain, and a flexibility to be applied to various apparatuses such as a camera module.

CLAIM OF PRIORITY

This application claims the benefit of Korean Patent Application No.2005-0071758 filed on Aug. 5, 2005, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric ultrasonic motor, andmore particularly, to a metal tube type piezoelectric ultrasonic motorhaving a piezoelectric element arranged on the exterior of a metal tube.

2. Description of the Related Art

In general, a piezoelectric ultrasonic motor includes a piezoelectricstator having a piezoelectric element attached thereto and a rotaryshaft contacting the piezoelectric stator to convert oscillation energyof the piezoelectric stator into rotation energy through frictionagainst the piezoelectric stator. The piezoelectric motor is classifiedinto several types.

As an example, U.S. patent application Publication No. 2005/0052098discloses a metal tube type piezoelectric ultrasonic motor.

As shown in FIGS. 1A and 1B, the metal type piezoelectric ultrasonicmotor disclosed in this document includes a hollow metal tube or housing14, four (4) piezoelectric elements 18, 20, 22 and 24 mounted on theexterior of the housing 14, a shaft 12 received inside the housing 14and having threads 17 formed on the outer periphery thereof, a nut 16with the inner periphery meshed with the threads 17 of the shaft 12 andthe outer periphery inserted into an inner space of the housing 14, anda bushing 28 for supporting the rotation of the shaft 17.

In this piezoelectric ultrasonic motor 10, the piezoelectric elements18, 20, 22 and 24 generate strain when an electric field is appliedthereto, which is transferred through threads in the inner periphery ofthe nut 16 to the threads 17 of the shaft 12, thereby to rotate theshaft 17.

However, since the conventional metal tube type piezoelectric ultrasonicmotor 10 produces rotational force through linear contact between thethreads of the nut 16 and those of the shaft 12, rotation number andtorque are low and thus sufficient power cannot be achieved.

Furthermore, the shaft 12 of the piezoelectric ultrasonic motor 10 ismoved into or out of the metal tube in response to the rotation of theshaft 12, which needs to be supported between the nut 16 and the bushing28. Then, the length of the shaft 12 should have an enough margin to belonger than the distance between the nut 16 and the bushing 28 (i.e.,the length of the metal tube). This disadvantageously increases amounting space for the piezoelectric ultrasonic motor.

Recently, owing to rapid development of IT industries, microscopiccamera modules to be mounted on a mobile phone and the like are gettingmore important. To meet demands of users, microscopic camera moduleshaving automatic focusing and/or optical zooming function are beingdistributed.

An electromotive motor or piezoelectric stator (or piezoelectricultrasonic motor) can be used to drive or transport a lens in such amicroscopic camera module. The piezoelectric ultrasonic motor using apiezoelectric element has been proposed as a lens driving actuator forthe microscopic camera module due to its merits such as rapid response,prevented reverse driving and high resolution in transport.

Accordingly, a piezoelectric ultrasonic motor adequate for lens drivingfor such a microscopic camera module is demanded.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an object of certain embodiments of thepresent invention is to provide a piezoelectric ultrasonic motor capableof increasing force and generating sufficient strain with stableactuation, and thus being applied to various apparatuses such as acamera module.

Another object of certain embodiments of the present invention is toprovide a piezoelectric ultrasonic motor and a lens driving apparatushaving the same capable of generating a sufficient level of strain andtorque necessary for transporting an object.

Further another object of certain embodiments of the present inventionis to provide a piezoelectric ultrasonic motor and a lens drivingapparatus having the same which can be provided in a module whilepreventing pollution of other parts.

According to an aspect of the invention for realizing the object, thereis provided a piezoelectric ultrasonic motor comprising: a piezoelectricstator including a metal tube with an inner space and a plurality ofpiezoelectric elements mounted on the outer circumference of the metaltube, the piezoelectric stator straining with an electric field appliedthereto; a rotary shaft including a rotation bar inserted into the innerspace of the metal tube, a rotation member provided around the rotationbar in contact with an upper or lower surface of the piezoelectricstator, the rotation member rotating in response to the strain of thepiezoelectric stator, and a power transmission member provided at oneportion of the rotation bar to transmit the rotation of the rotationmember to an object to be transported; and a power supply for applying asupply voltage necessary for the actuation of the piezoelectric stator.

Preferably, the rotation member includes an upper rotation membercontacting the upper surface of the piezoelectric stator and a lowerrotation member contacting the lower surface of the piezoelectricstator.

Preferably, the rotary shaft further includes a friction member fixed toa surface of the rotation member contacting the piezoelectric stator,and wherein the rotary shaft rotates through face contact between thepiezoelectric stator and the friction member.

Here, the friction member is preferably made of Poly-Ether-Ether-Ketone(PEEK).

Preferably, the friction material is made of alumina, and wherein thecontact surface of the piezoelectric stator contacting the frictionmember is fixedly provided with a contact member made of alumina or analumina coat.

Preferably, the rotary shaft further includes a preload member forpressing the rotation member toward the piezoelectric stator.

Preferably, the power supply applies the electric field to a nodal pointof the piezoelectric stator.

The piezoelectric ultrasonic motor may further comprise a housing forreceiving the piezoelectric stator and the rotary shaft.

The piezoelectric ultrasonic motor may further comprise a holder forsupporting the piezoelectric stator at a nodal point, wherein the holderis seated in an opening of the housing.

Preferably, the metal tube comprises a hollow tube having a circular orpolygonal cross section, and wherein seating portions are formed on theouter circumference of the metal tube to mount the piezoelectricelements.

More preferably, the metal tube has a quadrangular cross-section, andeach of the piezoelectric elements is mounted on each outer face of themetal tube.

Preferably, the piezoelectric elements have polarization directedoutward from the center of the piezoelectric stator.

Alternatively, the piezoelectric elements have polarization directedtoward the center from outside of the piezoelectric stator.

More preferably, the power supply applies supply voltages to thepiezoelectric elements with a phase difference of 90° in their order ina clockwise or counterclockwise direction.

Preferably, adjacent two of the piezoelectric elements have polarizationdirected from outside of the piezoelectric stator to the center, theother adjacent two of the piezoelectric elements have polarizationdirected outward from the center of the piezoelectric stator.

More preferably, the power supply applies supply voltages of the samephase to opposing piezoelectric elements but supply voltages of a phasedifference of 90° to adjacent piezoelectric elements.

Preferably, a friction material of high friction coefficient may becoated on the contact surface of the rotation member contacting thepiezoelectric stator.

Preferably, the power transmission member may be a lead screw or gearformed at one portion of the rotation bar.

Furthermore, it is preferable that the power transmission member may bea belt or chain provided at one portion of the rotation bar.

According to another aspect of the invention for realizing the object,there is provided a piezoelectric ultrasonic motor comprising: apiezoelectric stator including a hollow metal tube having a quadrangularcross section and four piezoelectric elements each installed in eachouter face of the metal tube, the piezoelectric stator straining with anelectric field applied thereto; a rotary shaft including a rotation barinserted into an inner space of the metal tube, an upper rotation memberprovided around the rotation bar in contact with an upper surface of thepiezoelectric stator, the rotation member rotating in response to thestrain of the piezoelectric stator, a lower rotation member adapted torestrain the rotation of the rotation bar and contacting a lower surfaceof the piezoelectric stator and a power transmission member provided atone portion of the rotation bar to transmit the rotation of the rotationmember to an object to be transported; and a power supply for applying asupply voltage necessary for the actuation of the piezoelectric stator.

Preferably, the rotary shaft further includes a friction member fixed toa surface of the upper rotation member contacting the piezoelectricstator, and wherein the rotary shaft rotates through face contactbetween the piezoelectric stator and the friction member.

Preferably, the friction member or the lower rotation member is made ofPoly-Ether-Ether-Ketone (PEEK).

Preferably, the friction member or the lower rotation member is made ofalumina, and wherein the contact surface of the piezoelectric statorcontacting the friction member is fixedly provided with a contact membermade of alumina or an alumina coat.

Preferably, the rotary shaft further includes a preload member forpressing the rotation member toward the piezoelectric stator.

Preferably, the preload member comprises a coil spring mounted on theouter circumference of the rotation bar or a step of the lower rotationmember.

The piezoelectric ultrasonic motor may further comprise aseparation-preventing member inserted into a recess formed at the otherportion of the rotation bar.

The piezoelectric ultrasonic motor may further comprise a washerprovided between the lower rotation member and the separation-preventingmember to minimize interference noise.

Preferably, the piezoelectric ultrasonic motor may further comprise aseparation-preventing holder for surrounding the outer circumference ofthe piezoelectric stator and a terminal of the power supply connected toa nodal point of the piezoelectric stator to prevent the terminals frombeing separated from the piezoelectric stator.

In the meantime, the piezoelectric ultrasonic motor may further comprisea housing for receiving the piezoelectric stator and the rotary shaft.

Furthermore, the piezoelectric ultrasonic motor may further comprise aholder for supporting the piezoelectric stator at a nodal point, whereinthe holder is seated in an opening of the housing.

Preferably, the piezoelectric elements have polarization directedoutward from the center of the piezoelectric stator.

Alternatively, the piezoelectric elements have polarization directedtoward the center from outside of the piezoelectric stator.

More preferably, the power supply applies supply voltages to thepiezoelectric elements with a phase difference of 90° in their order ina clockwise or counterclockwise direction.

Preferably, adjacent two of the piezoelectric elements have polarizationdirected from outside of the piezoelectric stator to the center, theother adjacent two of the piezoelectric elements have polarizationdirected outward from the center of the piezoelectric stator.

More preferably, the power supply applies supply voltages of the samephase to opposing piezoelectric elements but supply voltages of a phasedifference of 90° to adjacent piezoelectric elements.

Preferably, a friction material of high friction coefficient may becoated on the contact surface of the rotation member contacting thepiezoelectric stator.

Preferably, the power supply applies the electric field to a nodal pointof the piezoelectric stator.

Preferably, the power transmission member may be a lead screw or gearformed at one portion of the rotation bar.

Furthermore, it is preferable that the power transmission member may bea belt or chain provided at one portion of the rotation bar.

According to further another aspect of the invention for realizing theobject, there is provided a lens driving apparatus comprising: apiezoelectric ultrasonic motor as described above and a lens unit havingat least one lens, the lens unit being transported forward and backwardvia the power transmission member of the piezoelectric ultrasonic motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1A is a perspective view illustrating a piezoelectric ultrasonicmotor of the prior art;

FIG. 1B is a cross sectional view of the piezoelectric ultrasonic motorshown in FIG. 1A;

FIG. 2 is an exploded perspective view illustrating a piezoelectricultrasonic motor according to a first embodiment of the invention;

FIG. 3 is a cutaway perspective view illustrating the cross section ofthe piezoelectric ultrasonic motor according to the first embodiment ofthe invention;

FIG. 4 is an exploded perspective view illustrating a piezoelectricultrasonic motor according to a second embodiment of the invention;

FIG. 5 is a perspective view illustrating important parts of thepiezoelectric ultrasonic motor according to the second embodiment of theinvention;

FIG. 6 is a perspective view illustrating the piezoelectric ultrasonicmotor according to the second embodiment of the invention;

FIG. 7 is an assembly view illustrating the piezoelectric ultrasonicmotor according to the second embodiment of the invention;

FIG. 8 is another assembly view illustrating the piezoelectricultrasonic motor according to the second embodiment of the invention;

FIG. 9 is a graph illustrating force-RPM distribution according to thematerial of a contact surface of the invention;

FIG. 10 is a schematic view illustrating poling directions and drivingsignals of piezoelectric elements according to four (4) phaseenergization of the invention;

FIG. 11 is a schematic view illustrating poling directions and drivingsignals of piezoelectric elements according to two (2) phaseenergization of the invention; and

FIG. 12 is a perspective view illustrating a lens driving apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown.

FIG. 2 is an exploded perspective view illustrating a piezoelectricultrasonic motor according to a first embodiment of the invention, andFIG. 3 is a cutaway perspective view illustrating the cross section ofthe piezoelectric ultrasonic motor according to the first embodiment ofthe invention.

In addition, FIG. 4 is an exploded perspective view illustrating apiezoelectric ultrasonic motor according to a second embodiment of theinvention, FIG. 5 is a perspective view illustrating important parts ofthe piezoelectric ultrasonic motor according to the second embodiment ofthe invention, FIG. 6 is a perspective view illustrating thepiezoelectric ultrasonic motor according to the second embodiment of theinvention, FIG. 7 is an assembly view illustrating the piezoelectricultrasonic motor according to the second embodiment of the invention,and FIG. 8 is another assembly view illustrating the piezoelectricultrasonic motor according to the second embodiment of the invention.

The present invention aims to provide a piezoelectric ultrasonic motorfor generating rotational force through face contact with an upper orlower surface of a tubular piezoelectric stator.

First, the first embodiment of the invention will be described withreference to FIGS. 2 and 3.

As shown in FIGS. 2 and 3, the first embodiment of the invention relatesto a piezoelectric ultrasonic motor 60 including a piezoelectric stator100 having piezoelectric elements 120, a rotary shaft 200 for rotatingin face contact with an upper surface 111 or lower surface 112 of thepiezoelectric stator 100 and a power supply 300.

As shown in FIG. 2, the piezoelectric stator 100 includes a hollow metaltube 110 made of metal and a plurality of piezoelectric elements 120mounted on the exterior of the metal tube 110.

The piezoelectric stator 100 generates strain when an electric field isapplied to the piezoelectric elements 120 by the power supply 300.

The metal tube 110 is made of a hollow tube having a circular orpolygonal cross section, and has seating portions formed on the exteriorthereof to seat the piezoelectric elements 120. That is, where the metaltube 110 has a polygonal cross section, the plate like piezoelectricelements 120 may be mounted on corresponding sides of the metal tube110. In case of the metal tube 110 having a circular cross section, themetal tube 110 may directly seat thereon piezoelectric elements havingan arc-shaped cross section or provided with planar seating portions formounting the plate like piezoelectric elements 120.

For instance, the metal tube 110 may be constructed of a hollow tubehaving a quadrangular cross section as shown in FIG. 2, and fourpiezoelectric elements 120 may be provided one for each side of themetal tube 110.

Here, the piezoelectric elements 120 may have a polarity directedoutward from the center of the piezoelectric stator 100 as shown in (a)and (b) of FIG. 10, or directed inward from outside of the piezoelectricstator 100 as shown in (c) and (d) of FIG. 10.

Alternatively, of the piezoelectric elements 120, two adjacent devices123 and 124 have a polarity directed from outside of the piezoelectricstator 100 toward the center but the other two adjacent devices 121 and122 have a polarity directed outward from the center of thepiezoelectric stator 100 as shown in FIG. 11.

With such a polarization direction, the piezoelectric elements 120 (121to 124) are strained according to phase difference applied from thepower supply 30 as described later, and thus exert forward or backwardrotation to the rotor 200.

As shown in FIGS. 2 and 3, the rotary shaft 200 includes a rotation bar210 inserted into the inner space of the metal tube 110, a rotationmember 220 in face contact with the upper surface 111 or the lowersurface 112 of the piezoelectric stator 100 and a power transmissionmember 230 provided at one portion of the rotation bar 210 to transmitthe rotational force from the rotation member 220 to an object to betransported.

The rotation member 220 provided around the rotation bar 210 is wheelshaped, and in response to the strain of the piezoelectric stator 100,rotates in face contact with the lower surface 112 of the piezoelectricstator 100. Alternatively, the rotation member 220 may be adapted torotate in face contact with the upper surface 111 of the piezoelectricstator 100.

The rotary shaft 200 may also include a friction member 250 that isfixed to one surface 221 of the rotation member 220 opposed to thepiezoelectric stator 100. The friction member 250 can enhance frictionalforce thereby increasing the rotational force of the piezoelectric motor60.

Then, the rotary shaft 200 rotates through the face contact between thelower surface 112 of the piezoelectric stator 100 and the upper surface251 of the friction member 250.

Alternatively, a friction material of high friction coefficient may becoated on the surface 221 of the rotation member 220, which contacts thepiezoelectric stator 100, in order to enhance contact force.

As an example, the friction member 250 or friction material may adoptPoly-Ether-Ether-Ketone (PEEK).

Alternatively, the friction member 250 or friction member may be made ofalumina and the contact surface 112 of the piezoelectric stator 100 incontact with the friction member 250 or friction material may be fixedlyprovided with a contact member (not shown) made of alumina or coatedwith alumina.

As shown in FIGS. 2 and 2, the piezoelectric ultrasonic motor 60 mayhave a rotation support member 260 to support the rotation of therotation bar 210. The rotation support member 260 is fixed at one end toa lower housing 420 and provided at the other end with a recess 261 forrotatably receiving a rotation protrusion 211 of the rotation bar 210.

Furthermore, the piezoelectric ultrasonic motor 60 optionally includes abushing 150 for receiving and supporting the upper surface 111 of thepiezoelectric stator 100. The bush 150 has a hole 151 formed in thecenter so that the rotation bar 210 can rotate through the hole 151.

Preferably, the rotary shaft 200 has a preload member 270 for pressingthe rotation member 220 toward the piezoelectric stator 100 to enhancethe contact force.

The preload member 270 may adopt for example a coil spring providedbetween the rotation support member 260 for supporting the rotation ofthe rotary shaft 200 and the lower housing 420 as shown in FIGS. 2 and3.

The power transmission member 230 is but not limited to a lead screwformed above the rotation bar 210. Rather, the power transmission member230 may adopt any configuration that can transmit the rotational forceof the rotary shaft 200.

For example, the power transmission member 230 may be a gear formed atone portion of the rotation bar 210 or a belt or chain provided at oneportion of the rotation bar 210.

The power transmission member 230 is adapted to transmit the rotationalforce from the rotary shaft 200 to an object, thereby linearly moving orrotating it.

As shown in FIGS. 2 and 3, the power supply 300 applies an externalsupply voltage having phase difference to the piezoelectric elements 120through terminals 310, by which the piezoelectric stator 100 can beenergized.

Each of the terminals 310 is preferably connected to a nodal point ofthe piezoelectric stator 100 to optimize oscillation efficiency.

FIGS. 4 to 8 show a piezoelectric ultrasonic motor 60 according to asecond embodiment of the invention.

As in the first embodiment, the piezoelectric ultrasonic motor 60 ofthis embodiment includes a piezoelectric stator 100, a rotary shaft 200and a power supply 300.

This embodiment is similar to the first embodiment, but rotation members220 and 240 are in face contact with upper and lower surfaces 111 and112 of the piezoelectric stator 100 in order to enhance contact forceand thus rotational force.

In particular, the second embodiment can produce a driving forcesignificantly greater than that of the first embodiment by employingfriction at both the upper and lower surfaces.

In order to avoid unnecessary repetition, like parts are designated withlike reference signs and their description is omitted.

The piezoelectric stator 100 has a similar construction to the firstembodiment, and includes a hollow metal tube 110 having a quadrangularcross section and four (4) piezoelectric elements 120 each installed inone outer surface of the metal tube 110. The piezoelectric stator 100generates strain whenever an electric field is applied to thepiezoelectric stator 120.

The power supply 300 applies an external supply voltage having phasedifference to the piezoelectric elements 120 through terminals 310 tothereby energize the piezoelectric stator 100. Each of the terminals 310is preferably connected to a nodal point of the piezoelectric stator 100to optimize oscillation efficiency.

The rotary shaft 200 of this embodiment includes a rotation bar 210inserted into an inner space 113 of the metal tube 110 and awheel-shaped rotation member 220 provided around the rotation bar 210.The rotation member 220 is in face contact with the upper surface 111 ofthe piezoelectric stator 100 to rotate in response to the strain of thepiezoelectric stator 100. The rotary shaft 200 also includes a lowerrotation member 240 mounted on the rotation bar 210 to restrainrotation. The lower rotation member 240 is in face contact at an uppersurface 241 with the lower surface 112 of the piezoelectric stator 100.The rotary shaft 200 also includes a power transmission member 230provided at one portion of the rotation bar 210 to transmit rotationforce from the rotation members 220 and 240 to an object to betransported.

Preferably, the rotary shaft 200 optionally includes a friction member250 fixed to the lower surface of the upper rotation member 220 toenhance rotation force of the piezoelectric ultrasonic motor 60. Here,the rotary shaft 200 rotates through face contact between the uppersurface 111 thereof and the lower surface 251 of the friction member250.

Alternatively, a friction material of high friction coefficient may becoated on the lower surface of the upper rotation member 220, whichcontacts the piezoelectric stator 100, in order to enhance contactforce.

As an example, the friction member 250 or friction material may adoptPoly-Ether-Ether-Ketone (PEEK).

Alternatively, the friction member 250 or friction member may be made ofalumina and the contact surface 111 of the piezoelectric stator 100 incontact with the friction member 250 or friction material may be fixedlyprovided with a contact member (not shown) made of alumina or coatedwith alumina.

Furthermore, the lower rotation member 240 may be made of PEEK oralumina.

The piezoelectric ultrasonic motor 60 as shown in FIGS. 4 and 6optionally includes a bushing 150 for assisting the rotary shaft 200 torotate smoothly when the rotary shaft 200 is assembled with an upperhousing 410.

Preferably, the rotary shaft 200 has a preload member 270 for pressingthe upper and lower rotation members 220 and 240 toward thepiezoelectric stator 100 to enhance the contact force.

The preload member 270 may adopt for example a coil spring mountedaround the rotation bar 210 or a step 242 of the lower rotation member240 as shown in FIG. 4.

Preferably, a separation preventing member 290 is inserted into a groove212 formed at a lower portion of the rotation bar 210 to prevent thecoil spring type preload member 270 from separating from the rotationbar. The separation preventing bar 290 may adopt an E-ring as shown inFIG. 4.

Between the lower rotation member 240 and the separation preventingmember 290, a washer 280 is provided to minimize interference.

In the meantime, the lower rotation member 240 is mounted so as to berestrained in rotation with respect to the rotation bar 210 as shown inFIGS. 4 and 5. For this purpose, the rotation bar 210 is provided with aflat cutaway part 211 and the lower rotation member 240 is provided witha planar part 243 corresponding to the cutaway part 211.

That is, the lower rotation member 240 is movable in the longitudinaldirection of the rotation bar 210 to enhance the contact force againstthe piezoelectric stator 100 through the elastic force of the preloadmember 270, but restrained in the rotation direction to transmit therotation force obtained through contact with the piezoelectric stator100 to the rotation bar 210.

The lower rotation member 240 also includes a protrusion 244 rotatablyreceived in an inner space 113 of the metal tube 110 as shown in FIG. 4.

Also, as shown in FIG. 8, a tip 213 of the rotation bar 210 is receivedrotatably in housings 430 and 440 to enable the rotary shaft 200 torotate stably.

The power transmission member 230 is but not limited to a lead screwformed above the rotation bar 210. Rather, the power transmission member230 may adopt any configuration that can transmit the rotational forceof the rotary shaft 200.

For example, the power transmission member 230 may be a gear formed atone portion of the rotation bar 210 or a belt or chain provided at oneportion of the rotation bar 210. The power transmission member 230 isadapted to transmit the rotational force from the rotary shaft 200 to anobject, thereby linearly moving or rotating it.

The piezoelectric ultrasonic motor 60 of this embodiment also includeshousings 410 and 420 as shown in FIGS. 2 and 3 or the housings 430 and440 as shown in FIGS. 7 and 8, which are adapted to receive thepiezoelectric stator 100 and the rotary shaft 200.

For example, as shown in FIGS. 2 and 3, the piezoelectric stator 100 andthe rotary shaft 200 are received between the upper and lower housings410 and 420, which are snap-coupled together through coupling members413 and 421. Here, the upper housing 410 has a hole 412 for applying asupply voltage to the power supply 300 and an opening 412 for exposingthe power transmission member 230 to the outside.

Alternatively, as shown in FIGS. 7 and 8, the piezoelectric stator 100and the rotary shaft 200 are received inside the housings 430 and 440,which are divided into right and left parts. Here, the housing 440 shownin FIGS. 7 and 8 is provided with an opening 441 for applying a supplyvoltage to the power supply 300.

Such structure of the housings 410, 420 or 430, 440 is merely anexample, and various types of housing may be provided to receive thepiezoelectric stator 100 and the rotary shaft 200.

With the housings 410, 420; 430, 440, the piezoelectric ultrasonic motor60 can be assembled into a module and thus applied to various driving ortransport apparatuses.

The housings 410 and 420; 430 and 440, when provided as above, give amerit that foreign materials such as dust produced between thepiezoelectric stator 100 and the rotation member 220 owing to frictionthereof does not soil other apparatuses.

As shown in FIG. 7, the piezoelectric ultrasonic motor 60 of thisembodiment also includes a holder 500 for supporting the nodal point ofthe piezoelectric stator 100 to prevent trembling owing to theoscillation of the piezoelectric stator 100.

The holder 500 may be hollow to surround the piezoelectric stator 100 oropened at a portion thereof.

The holder 500 is be fixed seated in recesses 442 (only one is shown) inFIG. 7. Alternatively, a pair of holders 500 are provided at two nodalpoints a shown in FIG. 8.

A separation preventing holder 510 is provided to surround thepiezoelectric stator 100 and the terminals 310 of the power supply 300connected to the nodal points of the piezoelectric stator 100 as shownin FIG. 7 in order to prevent the terminals 310 from separating from thepiezoelectric stator 100.

The separation preventing holder 510 may be made of an elastic materialsuch as rubber to absorb shaking or trembling due to the oscillation ofthe piezoelectric stator 100.

Now the operation of the power supply 300 according to certainembodiments of the invention will be described with reference to FIGS.10 and 11.

FIG. 10 shows drive signals for applying supply voltages with a phasedifference of 90° in a clockwise or counterclockwise direction accordingto a four (4) phase energization mode.

Here, (a) and (b) of FIG. 10 indicate the polarization of first tofourth piezoelectric elements 121 to 124 are directed outward from arotary shaft in the center of a piezoelectric stator 100, (c) and (d) ofFIG. 10 indicate the polarization of the first to fourth piezoelectricelements 121 to 124 are directed to the center of the piezoelectricstator 100 from outside.

The power supply 300 applies supply voltages to the piezoelectricelements 121 to 124 with a phase difference of 90° in a clockwise orcounterclockwise direction, whereby the piezoelectric stator 100 isstrained. This as a result rotates the rotation members 220 and 240 ofthe rotary shaft 200 in face contact with the upper and lower surfacesof the piezoelectric stator 100.

First, as shown in FIG. 1 (a), the power supply 300 has a drive circuitto apply a positive sine wave +sin, a positive cosine wave +cos, anegative sine wave −sin and a negative cosine wave −cos to the first tofourth piezoelectric elements 121 to 124, with a phase difference of 90°in their order of clockwise direction, respectively.

As shown in FIG. 10 (b), the drive circuit of the power supply 300 isdesigned to apply a positive sine wave +sin, a positive cosine wave+cos, a negative sine wave −sin and a negative cosine wave −cos to thefirst piezoelectric element 121, the fourth piezoelectric element 124,the third piezoelectric element 123 and the second piezoelectric element122, with a phase difference of 90° in their order of counterclockwisedirection, respectively.

The power supply 300 as shown FIG. 10 (a) and (b) adopts a single drivecircuit to apply supply voltages with a phase difference of 90° to thepiezoelectric elements 121 to 124.

With such a drive circuit, the power supply 300 can rotate the rotationmembers 220 and 240 of the rotary shaft 200 in a clockwise orcounterclockwise direction, whereby the piezoelectric motor 60 ofcertain embodiments of the invention can rotate forward or backward.

FIG. 10 (c) and (d) show the same driving mechanism as FIG. 10 (a) and(b) except for different polarizing direction of the piezoelectricelements 121 to 124.

That is, as shown in FIG. 10 (c), the drive circuit of the power supply300 may be designed to apply a positive sine wave +sin, a positivecosine wave +cos, a negative sine wave −sin and a negative cosine wave−cos to the first to fourth piezoelectric elements 121 to 124, with aphase difference of 90° in their order of clockwise direction,respectively.

Also, as shown in FIG. 10 (d), the drive circuit of the power supply 300is designed to apply a positive sine wave +sin, a positive cosine wave+cos, a negative sine wave −sin and a negative cosine wave −cos to thefirst piezoelectric element 121, the fourth piezoelectric element 124,the third piezoelectric element 123 and the second piezoelectric element122, with a phase difference of 90° in their order of counterclockwisedirection, respectively.

As in FIG. 10 (a) and (b), the power supply 300 for producing drivesignals shown in FIG. 10 (c) and (d) adopts a single drive circuit toapply supply voltages to the piezoelectric elements 121 to 124 with aphase difference of 90° in a clockwise or counterclockwise direction.With the drive circuit, the power supply 300 can rotate the rotationmembers 220 and 240 of the rotary shaft 200 clockwise orcounterclockwise, whereby the piezoelectric motor 60 of certainembodiments of the invention can rotate forward or backward.

This disclosure adopting the four phase energization mode has a meritthat a ground part is not required in addition.

The piezoelectric motor 60 of this invention can be actuated in a two(2) phase energization mode also.

FIG. 11 illustrates driving signals according to two phase energizationof the invention.

As shown in FIG. 11, adjacent two devices 123 and 124 of the first tofourth piezoelectric elements 121 to 124 have a polarization directedfrom outside the piezoelectric stator 100 to the center, and the otheradjacent two devices 121 and 122 have a polarization directed outwardfrom the center of the piezoelectric stator 100.

Where the piezoelectric elements 121 to 124 are polarized as above, thepower supply 300 applies supply voltages with the same phase to twoopposing piezoelectric elements and supply voltages with a phasedifference of 90° or −90° to adjacent piezoelectric elements.

For example, as shown in FIG. 11, the power supply 300 may be providedwith a drive circuit for applying a positive sine wave +sin, a positivecosine wave +cos, a negative sine wave −sin and a negative cosine wave−cos to the first to fourth piezoelectric elements 121 to 124, with aphase difference of 90° in their order of clockwise direction,respectively.

Alternatively, the drive circuit of the power supply 300 may be designedto apply a positive sine wave +sin, a negative cosine wave −cos, anegative sine wave −sin and a positive cosine wave +cos to the first tofourth piezoelectric element 121 to 124, with a phase difference of 90°in their order of clockwise direction, respectively.

That is, to produce the drive signals as shown in FIG. 11, the powersupply 300 energizes the piezoelectric elements 121 to 124 by applyingsupply voltages with the same phase to two opposing piezoelectricelements of and supply voltages with a phase difference of 90° or −90°to adjacent piezoelectric elements.

With the drive circuit as above, the power supply 300 can rotate therotation members 220 and 240 of the rotary shaft 200 clockwise orcounterclockwise, whereby the piezoelectric motor 60 of certainembodiments of the invention can rotate forward or backward.

FIG. 9 is graphs illustrating force-RPM distribution according to thematerial of a contact surface of the invention, in which a supplyvoltage of 16 Vp-p with an input frequency of 140 kHz is appliedaccording to the four phase energization mode as shown in FIG. 10.

Here, blocks “PEEK” indicate force and RPM in a case where PEEK is usedin the friction member 250 fixed to the upper rotation member 220, thepiezoelectric stator surfaces made of Steel Use Stainless (SUS) are usedas the upper and lower surfaces 111 and 112 of the piezoelectric stator100 without using any friction material, and PEEK is used in the lowerrotation member 240.

Blocks “ALUMINA” indicate force and RPM in a case where alumina is usedfor the friction member 250 fixed to the upper rotation member 220,contact members (not shown) made of alumina are fixed respectively tothe upper and lower surfaces 111 and 112 of the piezoelectric stator100, and alumina is used for the lower rotation member 240.

By using contact at both sides and employing the friction member 250according to the second embodiment of the invention, it is possible toproduce rotation number of 3,500 RPM or more, which is significantlyhigher than 500 RPM to 600 RPM of the prior art. As a result, asufficient amount of strain necessary for transport can be produced.

Furthermore, a force of about 0.010 N or more is obtained at a distanceof 5 mm, and thus a torque necessary for transport can be produced at asufficient level.

Therefore, as merits of this invention, strain and torque necessary forthe transport of an object can be generated at a sufficient level.

FIG. 12 is a perspective view illustrating a lens driving apparatus 50comprising a piezoelectric ultrasonic motor of the invention. 61 Thelens driving apparatus 50 includes a piezoelectric ultrasonic motor 60having a construction as described above and a lens unit 610 to betransported forward and backward by the power transmission member 230 ofthe piezoelectric ultrasonic motor 60.

Here, the lens unit 610 includes at least one lens 612 mounted inside alens barrel 611, which engages with the lead screw of the powertransmission member 230 to move linearly and vertically in response tothe rotation of the power transmission member 230.

Preferably, the lens driving apparatus 50 includes a guide member 620for guiding the lens barrel 611 to realize movement along the opticalaxis.

In the meantime, the piezoelectric ultrasonic motor 60 and the lens unit610 may be provided inside a housing 630 as a camera module.

The lens driving apparatus 50 including the piezoelectric ultrasonicmotor 60 of the invention can generate a great force and a largerotation number, and thus provide a sufficient level of strain andtorque necessary for transporting a lens.

As set forth above, the piezoelectric ultrasonic motor of according tocertain embodiments of the invention can stably operate to generateenhanced force and sufficient strain and have a flexibility to beapplied to various apparatuses such as a camera module.

Furthermore, the piezoelectric stator and the rotary shaft are in facecontact with each other to generate a sufficient level of strain andtorque necessary for transporting an object. In particular, with therotary shaft in face contact with both the upper and lower surfaces ofthe piezoelectric stator, the piezoelectric ultrasonic motor canadvantageously achieve a high driving torque and rotation number.

In addition, by using a suitable material such as PEEK and alumina, itis possible to enhance contact force between the piezoelectric statorand the rotation member thereby producing a piezoelectric ultrasonicmotor having a sufficient level of driving torque and rotation number.

According to this invention, the piezoelectric ultrasonic motor can beprovided in a module, and thus be easily applied to various apparatuses.When the piezoelectric ultrasonic motor is installed inside a housing,it is possible to prevent other parts from being polluted by foreignmaterials generating from friction and abrasion.

Furthermore, the holder is provided to support the nodal point of thepiezoelectric stator thereby to enhance the oscillation efficiency ofthe piezoelectric stator as well as prevent shaking of the piezoelectricstator.

Moreover, certain embodiments of the invention can adopt variousenergization modes such as two or four phase energization. Inparticular, the four phase energization mode can advantageously excludea structure for grounding.

While the present invention has been shown and described in connectionwith the preferred embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A piezoelectric ultrasonic motor comprising: a piezoelectric statorincluding a metal tube with an inner space and a plurality ofpiezoelectric elements mounted on the outer circumference of the metaltube, the piezoelectric stator straining with an electric field appliedthereto; a rotary shaft including a rotation bar inserted into the innerspace of the metal tube, a rotation member provided around the rotationbar in contact with an upper or lower surface of the piezoelectricstator, the rotation member rotating in response to the strain of thepiezoelectric stator, and a power transmission member provided at oneportion of the rotation bar to transmit the rotation of the rotationmember to an object to be transported; and a power supply for applying asupply voltage necessary for the actuation of the piezoelectric stator.2. The piezoelectric ultrasonic motor according to claim 1, wherein themetal tube comprises a hollow tube having a circular or polygonal crosssection, and wherein seating portions are formed on the outercircumference of the metal tube to mount the piezoelectric elements. 3.The piezoelectric ultrasonic motor according to claim 2, wherein themetal tube has a quadrangular cross section, and each of thepiezoelectric elements are mounted on each outer face of the metal tube.4. The piezoelectric ultrasonic motor according to claim 1, wherein therotation member includes an upper rotation member contacting the uppersurface of the piezoelectric stator and a lower rotation membercontacting the lower surface of the piezoelectric stator.
 5. Thepiezoelectric ultrasonic motor according to claim 1, wherein the rotaryshaft further includes a friction member fixed to a surface of therotation member contacting the piezoelectric stator, and wherein therotary shaft rotates through face contact between the piezoelectricstator and the friction member.
 6. The piezoelectric ultrasonic motoraccording to claim 5, wherein the friction member is made ofPoly-Ether-Ether-Ketone (PEEK).
 7. The piezoelectric ultrasonic motoraccording to claim 5, wherein the friction material is made of alumina,and wherein the contact surface of the piezoelectric stator contactingthe friction member is fixedly provided with a contact member made ofalumina or an alumina coat.
 8. The piezoelectric ultrasonic motoraccording to claim 1, wherein the rotary shaft further includes apreload member for pressing the rotation member toward the piezoelectricstator.
 9. The piezoelectric ultrasonic motor according to claim 1,wherein the power supply applies the electric field to a nodal point ofthe piezoelectric stator.
 10. The piezoelectric ultrasonic motoraccording to claim 1, further comprising a housing for receiving thepiezoelectric stator and the rotary shaft.
 11. The piezoelectricultrasonic motor according to claim 10, further comprising a holder forsupporting the piezoelectric stator at a nodal point, wherein the holderis seated in an opening of the housing.
 12. A piezoelectric ultrasonicmotor comprising: a piezoelectric stator including a hollow metal tubehaving a quadrangular cross section and four piezoelectric elements eachinstalled in each outer face of the metal tube, the piezoelectric statorstraining with an electric field applied thereto; a rotary shaftincluding a rotation bar inserted into an inner space of the metal tube,an upper rotation member provided around the rotation bar in contactwith an upper surface of the piezoelectric stator, the rotation memberrotating in response to the strain of the piezoelectric stator, a lowerrotation member adapted to restrain the rotation of the rotation bar andcontacting a lower surface of the piezoelectric stator and a powertransmission member provided at one portion of the rotation bar totransmit the rotation of the rotation member to an object to betransported; and a power supply for applying a supply voltage necessaryfor the actuation of the piezoelectric stator.
 13. The piezoelectricultrasonic motor according to claim 12, wherein the rotary shaft furtherincludes a friction member fixed to a surface of the upper rotationmember contacting the piezoelectric stator, and wherein the rotary shaftrotates through face contact between the piezoelectric stator and thefriction member.
 14. The piezoelectric ultrasonic motor according toclaim 13, wherein the friction member or the lower rotation member ismade of Poly-Ether-Ether-Ketone (PEEK).
 15. The piezoelectric ultrasonicmotor according to claim 13, wherein the friction member or the lowerrotation member is made of alumina, and wherein the contact surface ofthe piezoelectric stator contacting the friction member is fixedlyprovided with a contact member made of alumina or an alumina coat. 16.The piezoelectric ultrasonic motor according to claim 12, wherein therotary shaft further includes a preload member for pressing the rotationmember toward the piezoelectric stator.
 17. The piezoelectric ultrasonicmotor according to claim 16, wherein the preload member comprises a coilspring mounted on the outer circumference of the rotation bar or a stepof the lower rotation member.
 18. The piezoelectric ultrasonic motoraccording to claim 17, further comprising a separation preventing memberinserted into a recess formed at the other portion of the rotation bar.19. The piezoelectric ultrasonic motor according to claim 18, furthercomprising a washer provided between the lower rotation member and theseparation preventing member to minimize interference noise.
 20. Thepiezoelectric ultrasonic motor according to claim 12, further comprisinga separation preventing holder for surrounding the outer circumferenceof the piezoelectric stator and a terminal of the power supply connectedto a nodal point of the piezoelectric stator to prevent the terminalsfrom being separated from the piezoelectric stator.
 21. Thepiezoelectric ultrasonic motor according to claim 12, further comprisinga housing for receiving the piezoelectric stator and the rotary shaft.22. The piezoelectric ultrasonic motor according to claim 21, furthercomprising a holder for supporting the piezoelectric stator at a nodalpoint, wherein the holder is seated in an opening of the housing.